Laser projector

ABSTRACT

A reflection-type laser projector ( 100 ) projects modulated laser beams outputted from a laser projection unit ( 40 ), on a screen, wherein a reflector ( 112 ) as a constituent of the screen ( 110 ) has reflection characteristics of reflecting, among the incident light, only laser beams of three colors of red, blue, and green, which are projected from the laser projection unit ( 40 ) and light in the neighboring wavelength band, and transmitting light in other wavelength bands, thereby preventing pictures on the screen ( 110 ) from becoming hard to be seen due to effects of indoor illumination or light from outdoors.

TECHNICAL FIELD

The present invention relates to laser projectors and, moreparticularly, to laser projectors which are employed in the opticalinformation field, utilizing coherent light.

BACKGROUND ART

In recent years, laser projectors which employ laser beams forprojection lights have been developed as projector devices. Areflection-type laser projector is disclosed in WO96/038757.

Hereinafter, such a prior art laser projector will be described.

FIG. 14( a) illustrates a structure of a prior art laser projector.

A prior art laser projector 600 has a laser projection unit 40 whichoutputs laser beams 41, and a screen 610 onto which the laser beams 41from the laser projection unit 40 are projected. The screen 610comprises a reflector 611 which reflects incident light such as thelaser beams 41, and a diffuser 612 which is placed at the front of thereflector 611 and diffuses light. In this case, ground glass or a groupof minute planar lenses having shallow concavo-convexes are used as thediffuser 612.

The laser projection unit 40 has a red laser 1, a blue laser 2, and agreen laser 3 as short-wavelength laser sources which emit laser beamsof three colors of red, blue, and green. The laser projection unit 40has corresponding mirrors 51 a, 52 a, and 53 a which reflect the threecolor laser beams P1, P2, and P3 from the short-wavelength lasersources, and a light modulation unit 20 which modulates the three colorlaser beams P1-P3, respectively.

FIG. 14( b) is a diagram illustrating a specific structure of the lightmodulation unit 20.

The light modulation unit 20 has liquid crystal cells 71, 72, and 73that modulate the lights from the corresponding lasers 1, 2, and 3 inaccordance with a video signal Sv, mirrors 51 b, 52 b, and 53 b thatreflect the laser beams P1, P2, and P3 which are reflected by themirrors 51 a, 52 a, and 53 a, respectively, and lens systems 61 a, 62 a,and 63 a which project the laser beams P1-P3 which are reflected by therespective mirrors 51 b, 52 b, and 53 b onto the corresponding liquidcrystal cells 71, 72, and 73. In FIG. 14( a), the liquid crystal cells71, 72, and 73 corresponding to the laser beams P1-P3 are abbreviated asliquid crystal cell 7, respectively, and the lens systems 61 a, 62 a,and 63 a corresponding to the laser beams P1-P3 are abbreviated as lenssystem 6 a, respectively.

The light modulation unit 20 further includes an optical device 8 thatoutputs the laser beams P1-P3 which are modulated by the liquid crystalcells 71, 72, and 73 with aligning the optical axes thereof with eachother, and a lens system 6 b that irradiates the laser beams which areoutputted from the optical device 8 onto the screen 610 with enlargingthose laser beams.

In this case, the red laser 1 outputs an output light of a semiconductorlaser as a red laser beam, and the blue laser 2 and the green laser 3output a blue laser beam and a green laser beam, respectively, utilizingwavelength conversion of the semiconductor laser light. As the screen610, a screen of gain 1 (a size of 90 inches) that is usually employedin a normal projector utilizing a mercury vapor lamp is employed.

Next, the operation will be described.

In this laser projector 600, the laser beams P1, P2, and P3 that areemitted from the respective lasers 1, 2, and 3 are projected onto theliquid crystal cell 7 through mirrors, and the laser beams that aremodulated by the liquid crystal cell 7 are projected onto the screen610.

More specifically, the red laser 1 exercises a continuous light emittingoperation, and the red laser beam P1 emitted therefrom is reflected bythe mirrors 51 a and 51 b to change the destination. Then, the red laserbeam P1 reflected by the mirrors 51 a and 51 b is projected by the lenssystem 61 a onto the liquid crystal cell 71 and is modulated by theliquid crystal cell 71 according to a video signal Sv. The red laserbeam P1 modulated by the liquid crystal cell 71 is inputted to theoptical device 8, and the red laser beam P1 that is outputted from theoptical device 8 is enlarged by the lens system 6 b to be projected onto the screen 610. Similarly, the blue laser beam P2 and the green laserbeam P3 that are emitted from the blue laser 2 and the green laser 3,respectively, are projected onto the corresponding liquid crystal cells72 and 73 through mirrors 52 a, 53 a, 52 b, and 53 b and lens systems 62a and 63 a, and the blue laser beam P2 and the green laser beam P3 whichare modulated by the corresponding liquid crystal cells are projectedonto the screen 610 through the optical device 8 and the lens system 6b.

Reflectance of the conventional screen 610 onto which the laser beamsare projected is kept approximately constant over a wavelength rangeexcept for a wavelength range where luminosity factor, i.e., sensitivityto light of human eyes, is significantly low (i.e., shorter than 400 nmor longer than 700 nm), as shown in FIG. 16.

With this screen 610, a person observes the light that is reflected orscattered by the screen 610 from the front face of the screen 610 (fromthe side of the laser projection unit). When the entire surface of thescreen 610 is full white, the screen 610 has the brightness ofapproximately 200 lux.

However, in cases where the laser beam 41 is projected on the screen 610and a person observes the laser beam 41 that is reflected by the screenfrom the front face of the screen 610, as described above, a phenomenonof “grayish-block” occurs, i.e., a phenomenon in which pictures on thescreen 610, which should be originally black, are seen as whitish whenfor example indoor illumination 30 or outdoor light 31 is applied to thescreen 610 as shown in FIG. 15. In FIG. 15, reference numeral 32 denotesa reflected illumination light, and numeral 42 denotes a reflected laserbeam.

To be more specific, in a situation where the brightness on the screen610 is 20 lux when the indoor illumination 30 is on, the contrast ofpictures on the screen 610 is 1000:1 when the indoor illumination 30 isturned off, while the contrast is lowered to 10:1 by turning on theindoor illumination 30.

The present invention is made to solve the above-mentioned problem, andit has for its object to provide a laser projector that can preventpictures on the screen from becoming hard to be seen due to effects ofindoor illumination or light from the outdoors.

SUMMARY OF THE INVENTION

To solve the above-mentioned problems, according to the presentinvention, a laser projector which modulates laser beams, and projectsthe modulated laser beams is provided, and comprises: short-wavelengthlaser sources that emit at least laser beams of three colors of red,blue, and green; a modulation unit that modulates the laser beams fromthe laser sources in accordance with a picture signal; and a screen ontowhich the modulated laser beams are projected, in which the screen hascharacteristics of reflecting incident light such that reflection peaksfor the incident light are located at the wavelengths of at least laserbeams of three colors of red, blue, and green, which are emitted fromthe short-wavelength laser sources, and at the neighboring wavelengths.

Thereby, even when, in addition to laser beams in which videoinformation is included, light other than these laser beams (forexample, indoor illumination or outside light such as sunlight) isapplied to the screen, it is possible to prevent the light other thanthe laser beams from being reflected by the screen, and consequently,prevent pictures on the screen from becoming hard to be seen because ofeffects of the light other than the laser beams.

Further, according to the present invention, the screen has a reflectorwhich reflects only at least laser beams of three colors of red, blue,and green emitted from the short-wavelength laser sources and lights inneighboring wavelength bands.

Thereby, it is possible to make the screen have the reflectioncharacteristics of reflecting only the laser lights and theirneighboring wavelengths, and transmitting light of other wavelengths(for example, indoor illumination or outside light such as sunlight).

Further, according to the present invention, the widths of theneighboring wavelengths of the wavelengths of at least laser beams ofthree colors of red, blue, and green reflected by the reflectors, arelonger than 3 nm and shorter than 10 nm, while having the wavelengths ofthe respective laser beams at their centers, respectively.

Thereby, it is possible to further prevent grayish-block phenomenon fromoccurring in pictures on the screen, thereby improving contrast of thepictures.

Further, according to the present invention, the reflector comprises adielectric multilayer film.

Thereby, it is possible to easily realize a screen that has reflectioncharacteristics of reflecting only wavelengths of laser beams and theneighboring wavelengths.

Further, according to the present invention, the reflector is formedusing a hologram recording material.

Thereby, it is possible to realize a screen that has reflectioncharacteristics of reflecting only wavelengths of laser beams and theneighboring wavelengths, and has high bending strength.

Further, according to the present invention, a projection room in whichthe screen is placed is illuminated by illumination light that hassignificantly low levels of wavelength components corresponding to thewavelengths of at least laser beams of three colors of red, blue, andgreen, which are emitted from the short-wavelength laser sources.

Thereby, it is possible to make grayish-block phenomenon hardly occur inpictures on the screen even when light other than the laser beams isapplied to the screen, thereby greatly improving the contrast of thepictures on the screen.

According to the present invention, a laser projector is provided whichmodulates laser beams, and projects the modulated laser beams, and whichcomprises: short-wavelength laser sources which emit at least laserbeams of three colors of red, blue, and green; a modulation unit thatmodulates the laser beams from the laser sources in accordance with apicture signal; a screen onto which the modulated laser beams areprojected; and an observing instrument for observing pictures which areprojected on the screen, in which the observing instrument is used toobserve pictures which are projected on the screen through a lighttransmitting member whose transmission peaks for incident light arelocated at the wavelengths of at least laser beams of three colors ofred, blue, and green, which are emitted from the short-wavelength lasersources, and at the neighboring wavelengths.

Thereby, it is possible to prevent grayish-block phenomenon fromoccurring in pictures on the screen when light other than the laserbeams is applied to the screen, in cases where a conventional laserprojector is employed.

According to the present invention, a laser projector is provided whichmodulates laser beams, and projects the modulated laser beams, and whichcomprises: short-wavelength laser sources that emits at least laserbeams of three colors of red, blue, and green; a modulation unit thatmodulates the laser beams from the laser sources in accordance with apicture signal; and a screen onto which the modulated laser beams areprojected, in which the screen has characteristics of transmittingincident light such that transmission peaks for the incident light arelocated at the wavelengths of at least laser beams of three colors ofred, blue, and green, which are emitted from the short-wavelength lasersources, and the neighboring wavelengths.

Thereby, even when light other than laser beams (for example, indoorillumination or outside light such as sunlight) in which videoinformation is included is applied to the screen, this light is nottransmitted through the screen and only at least laser beams of threecolors of red, blue, and green are transmitted, whereby it can beprevented that pictures become hard to be seen, even in a rear-typelaser projector.

Further, according to the present invention, the screen has an absorberthat transmits at least laser beams of three colors of red, blue, andgreen, which are emitted from the short-wavelength laser sources andlights in a neighboring wavelength band, and lights in a wavelength bandwhere luminosity factor is significantly low.

Thereby, it is possible to make the screen have transmissioncharacteristics of reflecting only laser lights and their neighboringwavelengths but absorbing lights of other wavelengths (for example,indoor illumination or outside light such as sunlight).

Further, according to the present invention, the wavelength rangeneighboring the wavelengths of at least laser beams of three colors ofred, blue, and green, which are transmitted by the absorber, is longerthan 3 nm and shorter than 10 nm, with the wavelengths of the respectivelaser beams being in the center.

Thereby, it is possible to further prevent grayish-block phenomenon fromoccurring in pictures on the screen, thereby improving the contrast ofthe pictures.

Further, according to the present invention, the absorber is formed bylaminating plural filters each cutting only lights with predeterminedwavelengths, among light incident on the absorber.

Thereby, it is possible to realize a screen that absorbs light otherthan lights with the wavelengths of laser beams and the neighboringwavelengths, and includes no grayish-block phenomenon in pictures on thescreen.

Further, according to the present invention, the laser sources arelocated on the rear side of the screen, and light projected from thelaser sources on the screen is observed from the front side of thescreen.

Thereby, it is possible to improve the contrast of pictures on thescreen even in the case of rear-projection type video projectors.

Further, according to the present invention, a projection room in whichthe screen is placed is illuminated by illumination light that hassignificantly low levels of wavelength components corresponding to thewavelengths of at least laser beams of three colors of red, blue, andgreen, which are emitted by the short-wavelength laser sources.

Thereby, it is possible to make grayish-block phenomenon hardly occur inpictures on the screen even when light other than the laser beams isapplied on the screen, thereby greatly improving the contrast of thepictures on the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a structure of a laser projectoraccording to a first embodiment of the present invention.

FIG. 2 is a diagram specifically illustrating a laser projection unit ofthe laser projector according to the first embodiment.

FIG. 3 is a diagram illustrating an example of a reflector according tothe first embodiment.

FIG. 4 is a diagram showing reflection characteristics of a screenaccording to the first embodiment.

FIG. 5 is a diagram illustrating a structure of a laser projectoraccording to a second embodiment of the present invention.

FIG. 6 is a diagram specifically illustrating a laser projection unit ofthe laser projector according to the second embodiment.

FIG. 7( a) is a diagram illustrating an example of a reflector accordingto the second embodiment.

FIG. 7( b) is a diagram showing away of producing the reflectoraccording to the second embodiment.

FIG. 8 is a diagram illustrating a structure of a laser projectoraccording to a third embodiment of the present invention.

FIG. 9( a) is a diagram illustrating an example of indoor illuminationaccording to the third embodiment.

FIG. 9( b) is a diagram illustrating another example of indoorillumination according to the third embodiment.

FIG. 10 is a diagram illustrating a structure of a laser projectoraccording to a fourth embodiment of the present invention.

FIG. 11 is a diagram specifically illustrating a laser projection unitof the laser projector according to the fourth embodiment.

FIG. 12 is a diagram showing transmission characteristics of a screenaccording to the fourth embodiment.

FIG. 13 is a diagram illustrating a structure of a laser projectoraccording to a fifth embodiment of the present invention.

FIG. 14( a) is a general view explaining a prior art laser projector.

FIG. 14( b) is a diagram illustrating a specific structure of a lightmodulation unit of the prior art laser projector.

FIG. 15 is a diagram for explaining a problem of the prior art laserprojector.

FIG. 16 is a diagram showing reflection characteristics of a screen ofthe prior art laser projector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiment 1

Hereinafter, a first embodiment of the present invention will bedescribed with reference to FIGS. 1 to 4.

A laser projector according to the first embodiment is a reflection-typelaser projector, in which the screen has reflection characteristics ofreflecting only wavelengths of laser beams which are outputted from thelaser projection unit and the neighboring wavelengths, and this laserprojector modulates the laser beams from the laser projection unit, andprojects the modulated laser beams on the screen having such reflectioncharacteristics.

FIG. 1 is a diagram for explaining a laser projector 100 according tothe first embodiment.

The laser projector 100 according to the first embodiment has a laserprojection unit 40 that outputs laser beams 41, and a screen 110 ontowhich the laser beams 41 from the projection unit 40 are projected.

According to the first embodiment, the screen 110 comprises a reflector111 which reflects, among lights incident on the screen 110, only lightswith specific wavelengths, i.e., only the laser beams that are outputtedfrom the laser projection unit 40 and lights in the neighboringwavelength band, and transmits lights with other wavelengths, and adiffuser 112 which is placed at the front of the reflector 111 anddiffuses light. As the diffuser 112, ground glass or a group of minuteplanar lenses having shallow concavo-convexes, or the like are employed,as in the prior art laser projector 600.

In this first embodiment, the laser projection unit 40 has a structuresubstantially similar to that of the prior art laser projector 600.Hereinafter, a brief description will be initially given of a laser thatis used in this first embodiment as a short-wavelength light source.

The read laser 1 emits light of a red semiconductor laser of 640 nm, asa red laser beam. The blue laser 2 and the green laser 3 performwavelength conversion for the output light from the semiconductor laser,thereby emitting a blue laser beam and a green laser beam.

In this embodiment, a 640 nm red semiconductor laser is used as the redlaser 1, and short-wavelength laser sources which subject the laseroutput from the semiconductor laser to light wavelength conversion areused as the blue laser 2 and the green laser 3. As a light wavelengthconversion element that performs the light wavelength conversion, anMgO-doped LiNbO3 substrate is employed. Since short-wavelength lasersources employed as the blue laser 2 and the green laser 3 are of thesame structure, the blue laser will be briefly described below.

The semiconductor laser used here has the wavelength of 930 nm and theoutput power of 600 mW. A blue light beam of 200 mW (the wavelength of465 nm) is obtained from this 600 mW semiconductor laser. Further, 200mW laser power output is obtained from the green laser, and 400 mW laserpower output is obtained from the red semiconductor laser. The laserbeams emitted from the corresponding lasers have stable lateral mode andpower, and good color reproducibility, and further, provide pictures ofgood contrast on the screen.

Next, a description is given of screen 110 in laser projector 100according to the first embodiment.

In this first embodiment, as the reflector 111 which is a constituent ofthe screen 110, a dielectric multilayer film is employed, for example.

The dielectric multilayer film is produced by alternately laminatingSiO₂ layers 111 a and TiO₂ layers 111 b as shown in FIG. 3.Approximately 50 pieces of SiO₂ layers 111 a and approximately 50 piecesof the TiO₂ layers 111 b are laminated.

FIG. 4 shows reflection characteristics of the reflector 111 comprisingthe dielectric multilayer film. The reflector 111 has reflectioncharacteristics of reflecting 95% of blue light (465 nm), green light(532 nm), and red light (635 nm) which are incident thereto, as shown inFIG. 4.

In the screen 110 which is produced by placing the diffuser 112 at thefront of the reflector 111 having the above-mentioned reflectioncharacteristics, acceptable wavelength ranges A for the respectivereflected lights in response to the incident lights that have thewavelengths of the respective laser outputs as their center wavelengths,have values within a predetermined range. Here, the acceptablewavelength ranges A are wavelength ranges which cover wavelengths atwhich the reflectance is higher than one-half of the reflectance (Rp) atthe center wavelength.

Preferably, this acceptable wavelength range A is longer than 3 nm andshorter than 10 nm. Hereinafter, grounds for the lower limit and upperlimit of the acceptable wavelength range will be briefly described.

When, for example, a projection is performed under the indoorillumination 30 as shown in FIG. 2 by the laser projector 100 accordingto the first embodiment, a laser beam 41 is projected onto the screen110 from the laser irradiation unit 40, and the laser beam 41 isreflected by the screen 110, while the irradiation light 31 from theindoor illumination 30 is hardly reflected by the screen 110 and onlythe wavelength component that is equivalent to a part of the laser lightis reflected by the screen. Consequently, it is possible to prevent thatpictures on the screen 110 become hard to be seen influenced by theillumination light 30 from the indoor illumination 30.

The reason why display of good contrast with less grayish-blockphenomenon in the pictures on screen can be thus obtained even in a roomhaving the irradiation light 31 is because the wavelength range of thelaser light emitted from the laser projection unit 40 is quite narrow.

For example, when the acceptable wavelength range A exceeds 10 nm, lightof indoor illumination or the like having components other than thewavelength components of the laser beams 41 emitted from the laserprojection unit 40 is reflected by the screen, and thereby pictures onthe screen 110 cause grayish-block phenomenon. Therefore, it isdesirable that the reflection wavelength range A should not exceed 10nm.

Besides, variations or changes in the lasing wavelength of the lasersare shorter than 2 nm even when variations in the environmentaltemperatures are considered. For example, when the red laser 1 has anindividual variation of 1 nm in the lasing wavelength and has awavelength change of 0.06 nm/° C. for temperature change, the variationwidth of the lasing wavelength becomes about 2 nm for the temperaturerange of 30° C. When the individual variation range (1 nm) in the lasingwavelength of the red laser 1 is added thereto, the wavelength variationrange of 3 nm is obtained for this red laser 1.

From the foregoing, it is desirable that the acceptable wavelength rangeA for the laser beam 41 that is reflected by the screen 110 in thisfirst embodiment should be a range that is longer than 3 nm and shorterthan 10 nm with the wavelength of the laser beam 41 at its center.

In this case, a result that the contrast of pictures on the screen isimproved about 10 times relative to the case of using the conventionalscreen is obtained.

Next, the function and effect will be described.

In the laser projector 100 according to the first embodiment, as in theprior art laser projector 600, laser beams P1, P2, and P3 that areemitted from the respective lasers 1, 2, and 3 are projected onto theliquid crystal cell 7 through mirrors, and the laser beams P1, P2, andP3 that have been modulated by the liquid crystal cell are projectedonto the screen 110.

In this first embodiment, only lights having the same wavelengthcomponents as those in the projected laser beams 41 which are emittedfrom the respective lasers, i.e., only blue light beam (465 nm), greenlight beam (532 nm), and red light beam (635 nm), and lights of theirneighboring wavelengths are reflected by the screen 110.

Therefore, even when the illumination light 31 of the indoorillumination 30 is incident on the screen 110 as shown in FIG. 2, lightsof almost all the wavelength components thereof pass through the screen,and the illumination light 132 that was reflected by the screen 110comprises only the same wavelength components as those in the laserbeams 41 emitted from the respective lasers among the wavelengthcomponents included in the illumination light 31.

According to the first embodiment described above, in thereflection-type laser projector 100 that projects modulated laser beamsoutputted from the laser projection unit 40 onto a screen, the reflector112 which is an element constituting the screen 110 is made to havereflection characteristics that reflect only laser beams of three colors(red, blue, and green) which are projected by the laser projection unit40 as well as lights in their neighboring wavelength band among theincident lights, and transmit lights in the other wavelength bands.Therefore, the ratio of light intensity of the projected laser light 142that has been modulated by the video signal, relative to the lightintensity of the light that is not modulated by the video signal such asthe illumination light 132 can be held at a large value, and therebypictures on the screen 110 can be prevented from becoming hard to beseen affected by the indoor illumination or lights from outdoors.

Further, in this first embodiment, the wavelength range of the lightswhich are reflected by the reflector 111 of the screen 110 is set to belonger than 3 nm and shorter than 10 nm, with the wavelengths of therespective laser beams which are outputted from the laser projectionunit 40 as their centers. Therefore, in consideration of actualwavelength variations in the lights emitted from the lasers, only thelights of projected laser outputs can be efficiently reflected on thescreen 110, and there by the contrast of the pictures on the screen isgreatly improved.

Embodiment 2

Hereinafter, a second embodiment of the present invention will bedescribed with reference to FIGS. 5 to 7.

A laser projector according to the second embodiment is provided with ascreen having a reflector constituted by a hologram recording material,in place of a screen having a reflector constituted by a dielectricmulti-layer film according to the first embodiment, and this laser willbe described in detail.

FIG. 5 is a diagram for explaining a laser projector 200 according tothe second embodiment.

A laser projector 200 according to the second embodiment has a laserprojection unit 40 which outputs laser beams 41, and a screen 210 ontowhich the laser beams 41 from the laser projection unit 41 areprojected, similarly as the laser projector 100 according to the firstembodiment.

According to the second embodiment, the screen 210 has a reflector 211which reflects lights with specific wavelengths, i.e., only thewavelengths of the laser beams that are outputted from the laserprojection unit 40 and their neighboring wavelengths among lightsincident on the screen 210, and transmits lights with other wavelengths,and a diffuser 212 which diffuses light, disposed at the front of thereflector 211. As the diffuser 212, ground glass or a group of planarlenses having shallow concavo-convexes are employed as in the prior artlaser projector 600.

In addition, according to the second embodiment, as a short-wavelengthlaser source of the laser projection unit 40, one which subjects laseroutputs from three kinds of solid lasers that emit lights of primarycolors to wavelength conversion is employed. This short-wavelength lasersource according to the second embodiment will be specifically describedhereinafter.

In this case, a solid laser using a Nd:YAG crystal is employed as eachof the solid lasers which emit laser beams with the wavelengths of 1320nm and 1064 nm, respectively, and a solid laser using a Nd:YVO4 crystalis employed as a solid laser which emits laser beam with the wavelengthof 914 nm. Further, in this second embodiment, as the short-wavelengthlaser source in the laser projection unit 40, one which converts theoutputs from these solid lasers into laser beams having their halfwavelength by means of a second harmonic generation circuit (not shown)which performs light wavelength conversion and outputs a red laser P1 of4 W (wavelength of 660 nm), a green laser P3 of 1 W (wavelength of 532nm), and a blue laser P2 of 1 W (wavelength of 457 nm) is employed.Here, since the wavelengths of laser outputs from the solid lasershardly change due to temperature changes, the utilization of solidlasers makes it possible to employ a reflector using a reflection filmof a narrow wavelength band having a narrow reflecting wavelength band.

Next, the screen 210 of the laser projector 200 according to the secondembodiment will be described in more detail.

In this second embodiment, the reflector 211 as the constituent of thescreen 210 is formed by using a hologram recording material. Theshort-wavelength laser source emits the red laser beam (the wavelengthof 660 nm), the green laser beam (the wavelength of 532 nm), and theblue laser beam (the wavelength of 457 nm). Thus, the reflector 211 hasreflection characteristics of selectively reflecting the incident bluelight (457 nm), green light (532 nm), and red light (660 nm).

Since the wavelengths to be reflected by the reflector 211 are three,i.e., 457 nm of blue, 532 nm of green, and 660 nm of red, three gratingsof different periods are formed one upon another in the hologramrecording material.

FIG. 7( a) shows the three gratings of different periods which areformed in the hologram recording material. Reference numeral 211 adenotes a first exposure layer which forms a grating with a firstperiod, numeral 211 b denotes a second exposure layer which forms agrating with a second period, and numeral 211 c denotes a third exposurelayer which forms a grating with a third period.

The three gratings with different periods are formed by performing threetimes of interference exposures to the hologram recording material, forexample, as shown in FIG. 7( b). In FIG. 7( b), reference charactersEp1˜Ep3 denote a pair of lights having the same phase, respectively,which are employed at the first to third interference exposures. Theselights Ep1˜Ep3 have different incident angles to the hologram recordingmaterial.

In addition, the diffuser 212 is placed at the front of the reflector211 as in the prior art, and diffuses lights outputted from thereflector 211. In this case, a group of minute planar lenses isemployed. By arranging the minute planar lenses each having thenumerical aperture of 0.1 and the diameter of 0.5 mm in one plane, aneffectively-operating diffuser with little loss can be obtained.

Further, the diffuser 212 can be formed not by arranging theabove-mentioned group of minute planar lenses on one side of thehologram recording material in which plural gratings are multiplexed,but by such as embossing the surface of the hologram recording materialin such a form that a group of minute planar lenses is arranged. Thus,it becomes possible to integrally form the reflector 211 and thediffuser 212, and consequently, it becomes possible to provide thescreen 210 having the above-mentioned reflection characteristics at alower cost.

Next, the function and effect will be described.

With the laser projector 200 according to the second embodiment, likethe laser projector 100 according to the first embodiment, the laserbeams P1, P2, and P3 which have been emitted from the correspondinglasers 1, 2, and 3 are projected on the liquid crystal cell 7 through amirror, and the laser beams P1, P2, and P3 which have been modulated bythe liquid crystal cell are projected on the screen 210.

According to the second embodiment, the screen 210 reflects only lightsof the same wavelength components as those of the projected laser beams41 which are emitted from the respective lasers, i.e., the blue light(457 nm), the green light (532 nm), and the red light (660 nm), andlights with the neighboring wavelengths, as shown in FIG. 6.

Therefore, as shown in FIG. 6, even when the illumination light 31 ofthe indoor illumination 30 is incident on the screen 210, lights of mostof its wavelength components pass through the screen, and reflectedillumination light 132 that has been reflected by the screen 210comprises only light of the same wavelength components as those of thelaser beams 41 emitted from the respective lasers, among the wavelengthcomponents included in the illumination light 31.

Consequently, it is possible to prevent pictures on the screen 210 frombecoming hard to be seen due to the effect of the illumination light 31of the indoor light 30.

According to the second embodiment, by using the solid laser as theshort-wavelength laser source of the laser projection unit 40, it ispossible to narrow the reflector acceptable wavelength range A of thescreen more than in the first embodiment. More specifically, since theacceptable wavelength range A can be set at 5 nm in this case, thecontrast of the pictures on the screen 210 is improved up to 20, ascompared to the case of utilizing the conventional screen.

As described above, the reflector 211 of the screen 210 according to thesecond embodiment is constructed so as to reflect, among the incidentlight, only lights with the wavelengths of the three color laser beams41 which are projected by the laser projection unit 40, and theneighboring wavelengths, while transmitting other wavelengths.Therefore, it is possible to prevent grayish-block phenomenon fromoccurring in the pictures on the screen 210 even when the indoorillumination is turned on.

Further, as the hologram recording material is used as the reflector 211of the screen 210 in the second embodiment, higher bending strength isobtained, and further, it is possible to integrally form the diffuser212 and the reflector 211, thereby providing the screen having theabove-mentioned reflection characteristics at a lower cost.

Embodiment 3

Hereinafter, a third embodiment of the present invention will bedescribed with reference to FIGS. 8 and 9.

A laser projector according to the third embodiment is identical to thelaser projector according to the first embodiment. In this thirdembodiment, there is employed, as an indoor illumination, one which usesa filter to interrupt lights of wavelengths corresponding to therespective laser outputs according to the first embodiment.

FIG. 8 is a diagram for explaining a laser projector 300 according tothe third embodiment.

The laser projector 300 according to the third embodiment has a laserprojection unit 40 which outputs laser beams 41, and a screen 110 ontowhich the laser beams 41 from the laser projection unit 40 areprojected, similarly as the laser projector 100 according to the firstembodiment.

Indoor illumination 330 according to the third embodiment emitsillumination light 331 from which the wavelengths corresponding to thelaser beams outputted from the laser projection unit 40, i.e., thewavelengths near 635 nm of the red laser beam, the wavelengths near 465nm of the blue laser beam, and the wavelengths near 532 nm of the greenlaser beam, are cut out.

Here, the indoor illumination 330 is obtained by affixing a filter 332that cuts out wavelength components corresponding to the laser beamsoutputted from the laser projection unit 40, surrounding a commerciallyavailable fluorescent lamp 331, for example as shown in FIG. 9( a).

The indoor illumination used in this third embodiment is not limited tothat shown in FIG. 9( a), but a cover for covering an illuminating lampsuch as a fluorescent lamp 341 may be provided with a filter for cuttingout wavelength components corresponding to the laser beams outputtedfrom the laser projection unit 40, for example as shown in FIG. 9( b).

When this indoor illumination 330 is placed in a projection room, theillumination light 331 is not reflected by the screen 110 but all thelights are transmitted through the screen 110 as shown in FIG. 8 becausethe wavelengths of the illumination light 331 from the indoorillumination 330, which are to be reflected by the screen 110, havepreviously been cut out. Accordingly, only the laser beams 41 which areprojected from the laser projection unit 40 are reflected by the screen110. Consequently, it is possible to more efficiently preventgrayish-block phenomenon from occurring in pictures on the screen 110.

More specifically, the contrast of the pictures on the screen isimproved up to 300 in a state where the illumination is turned on, ascompared to the case of using the conventional screen.

As described above, according to the third embodiment, the reflector 111of the screen 110 has a construction that reflects, among the incidentlights, only the three color laser beams 41 which are projected from thelaser projection unit 40 and lights with the neighboring wavelengths,and transmits the other wavelengths, and further, the indoorillumination 330 of the projection room in which the laser projector 40is placed outputs the illumination light 331 from which the wavelengthcomponents corresponding to the laser beams outputted from the laserprojection unit 40 have been cut out. Therefore, it is possible tocompletely prevent grayish-block phenomenon from occurring in thepictures on the screen 110 even when the indoor illumination 330 isturned on.

In this third embodiment the indoor illumination placed in theprojection room is one which uses a filter to cut out the specificwavelength components from the light of the fluorescent lamp. Forexample a laser may be used as the indoor illumination.

For example, by using lasers which emit laser beams with wavelengths of470 nm, 550 nm, and 620 nm as the indoor illumination, the selectivityof wavelengths of the light reflected by the screen is increased more,whereby the contrast of the pictures on the screen 110 is improved, andalso it is possible to completely prevent grayish-block phenomenon fromoccurring in the pictures on the screen 110.

It is also possible to employ, as the indoor illumination 330 placed inthe projection room, an LED with a different emission wavelength fromthe wavelengths of the laser beams 41 outputted from the laserprojection unit 40. Thereby, the indoor illumination 330 to be placed inthe projection room can be provided at a lower cost because the LEDillumination is less expensive.

Further, while in this third embodiment the laser projector has the samestructure as that of the laser projector according to the firstembodiment, the laser projector according to the third embodiment mayhave the same structure as that of the laser projector according to thesecond embodiment. Also in this case, the same effect can be obtained.

Embodiment 4

Hereinafter, a fourth embodiment of the present invention will bedescribed with reference to FIGS. 10 to 12.

A laser projector according to the fourth embodiment is arear-projection type laser projector which projects laser beams from therear surface of the screen, and the screen has light transmissioncharacteristics of transmitting lights with wavelengths of the laserbeams that are outputted from the laser projection unit and theneighboring wavelengths, and lights in a wavelength band where theluminosity factor is significantly low.

FIG. 10 is a diagram for explaining a laser projector 400 according tothe fourth embodiment.

The laser projector 400 according to the fourth embodiment has a laserprojection unit 50 which outputs laser beams 51, and a screen 410 ontowhich the laser beams 51 from the laser projection unit 50 areprojected.

In this fourth embodiment, the screen 410 comprises an absorber 413which transmits, among light incident on the screen 410, lights withspecific wavelengths i.e., lights with the wavelengths corresponding tolaser beams that are outputted from the laser projection unit 50 and theneighboring wavelengths, and lights in a wavelength band where theluminosity factor is significantly low, and absorbs lights with otherwavelengths, and a diffuser 412 which is placed at the front of theabsorber 413 and diffuses lights. The diffuser 412 may comprise groundglass or a group of minute planar lenses having shallowconcavo-convexes, or the like.

The laser projection unit 50 modulates the respective laser beams ofthree colors, which are emitted from the short-wavelength laser sources,and projects the modulated laser beams on the screen 410 whileperforming horizontal and vertical scanning. That is, the laserprojection unit 50 has red, blue, and green lasers 1, 2, and 3 which areshort-wavelength laser sources that emit three colors (red, blue, andgreen) of laser beams, and a modulation unit 54 which comprisesmodulation circuits 54 a˜54 c corresponding to the laser beams P1˜P3,which modulate the three colors of laser beams P1˜P3 outputted from theshort-wavelength laser sources, respectively. The laser projection unit50 has horizontal deflection units 55 a, 55 b, and 55 c using polygonmirrors, which deflect the corresponding modulated laser beams so as tobe subjected to horizontal scanning on the screen, and verticaldeflection units 56 a, 56 b, and 56 c using galvanic mirrors, whichdeflect the corresponding modulated laser beams to be subjected tovertical scanning on the screen. In this fourth embodiment, the redlaser 1 emits, as a read laser beam, output light from a 640 nm redsemiconductor laser, and the blue laser 2 and the green laser 3 emit ablue laser beam and a green laser beam by performing wavelengthconversion to the light emitted from the semiconductor laser.

In this fourth embodiment, as in the first embodiment, the 640 nm redsemiconductor laser is employed as the red laser 1, and short-wavelengthlaser sources which perform light wavelength conversion to the laseroutput from the semiconductor laser are employed as the blue laser 2 andthe green laser 3. In addition, as a light wavelength conversion elementthat performs the light wavelength conversion, an MgO-doped LiNbO₃substrate is employed. Because the short-wavelength laser sources whichare used as the blue laser 2 and the green laser 3 have the samestructure, one used as the blue laser will be briefly described.

The semiconductor laser used herein is one having the wavelength of 930nm and the power of 600 mW. The blue light of 200 mW (the wavelength is465 nm) is obtained by this 600 mW semiconductor laser. Further, thegreen laser provides a laser output of 200 mW, and the red semiconductorlaser provides a laser output of 400 mW. The laser beams emitted fromthe respective lasers have stable lateral mode and power, and good colorreproducibility, as well as realize good contrast of pictures on thescreen.

Next, the screen 410 of the laser projector 400 according to the fourthembodiment will be described.

FIG. 12 is a diagram showing transmission characteristics of the screen410.

As described above, the screen 410 according to the fourth embodimentcomprises the absorber 413 and the diffuser 412. The absorber 413 hastwo color filters which are placed one upon another so as to have 90% oflight transmittance for the respective wavelengths of the three colorlaser beams which are outputted by the laser projection unit 50, i.e.,457 nm of blue, 532 nm of green, and 650 nm of red, as shown in FIG. 12.In FIG. 12, as the two filters, a filter having the absorption peak at505 nm and a filter having the absorption peak at 590 nm are shown as anexample. Although this absorber 413 also transmits the wavelengthsshorter than 400 nm and the wavelengths longer than 700 nm, lights inthese wavelength bands can be visually neglected even when they aretransmitted through the absorber 413 because the luminosity factor issignificantly low in these wavelengths.

On the other hand, the diffuser 412 of the screen 110 diffuses thelights that are transmitted by the absorber 413 to some extent. In thiscase, ground glass having shallow concavities and convexities isemployed.

When the screen 410 having such transmission characteristics is used,only the laser beams 51 which are projected by the laser projection unit50 and lights in the neighboring wavelength band, and lights in awavelength band where the luminosity factor is significantly low aretransmitted through the absorber 413, and lights in other wavelengthbands are absorbed by the absorber 413, as shown in FIG. 11.Consequently, it is possible to considerably prevent grayish-blockphenomenon from occurring in pictures on the screen 410.

As described above, less grayish-block phenomenon appears in pictures onthe screen and good contrast display can be obtained even in a roomwhere the illumination light 31 is present as described above. This isbecause the lasing wavelength range of the laser beams which areoutputted from the laser projection unit 50 is extremely narrow.

For example, when the acceptable wavelength range B of wavelengths thatare transmitted through the absorber 413, with the wavelength of theoutput beam from each laser being a center wavelength, exceeds 10 nm,lights of wavelength components which can be sensed by human eyes otherthan the wavelength components of the laser beams 51 outputted by thelaser projection unit 50 pass through the absorber 413, and therebygrayish-block phenomenon would appear in pictures on the screen 410.Therefore, it is preferable that the acceptable wavelength range B oflights which pass through the absorber 413 should be shorter than 10 nm.

In addition, variations or changes in the lasing wavelength of the laserare smaller than 2 nm even when variations in environmental temperatureare considered. For example, when the red laser 1 has individualvariations of 1 nm with regard to the lasing wavelength and a wavelengthchange of 0.06 nm/° C. occurs due to temperature change, the range ofvariations in the lasing wavelength within, for example, a temperaturerange of 30° C. is approximately 2 nm, and when the individual variationrange of 1 nm for the lasing wavelength of the red laser 1 is addedthereto, the wavelength variation range of this laser becomes 3 nm.

From the foregoing, it is desirable that the acceptable wavelength rangeB of the laser beam 51 which is transmitted through the screen 410according to the fourth embodiment should be longer than 3 nm andshorter than 10 nm, with the wavelength of the laser beam 51 being inthe center.

In this case, more specifically, the contrast of the pictures on thescreen is improved about 10 times as compared to the case of utilizingthe conventional screen.

Next, the function and effect will be described.

In the laser projector 400 according to the fourth embodiment, the laserbeams P1, P2, and P3 which are emitted from the corresponding lasers 1,2, and 3 are modulated by the corresponding modulation circuits 54 a˜54c, respectively, in accordance with a video signal (not shown), and themodulated laser beams are projected on the rear surface of the screen410 via the horizontal deflection units 55 a˜55 c and the verticaldeflection unit 56.

More specifically, the red laser 1 performs a continuous light-emittingoperation, and a video signal is superimposed on the laser beam P1emitted from the red laser 1 by the modulation circuit 54 a, to scan thescreen 410 with the horizontal deflection unit 55 a using a polygonmirror and the vertical deflection unit 56 using a galvanic mirror.Similarly, the blue laser beam P2 and the green laser beam P3 which areemitted from the blue laser 2 and the green laser 3, respectively, arealso subjected to modulation to superimpose the video signal thereon bythe modulation circuits 54 b and 54 c, and then projected on the screen410.

Then, among the laser beams 51 and the illumination light 31 from theindoor illumination 30, lights with wavelengths near 465 nm of the bluelaser beam, 532 nm of the green laser beam, and 635 nm of the red laserbeam, and lights with wavelengths which are shorter than 400 nm andlonger than 700 nm in which the luminosity factor is significantly low,are transmitted through the absorber 413 of the screen 410, and thetransmitted laser beams 452 and the transmitted illumination light 432are diffused by the diffuser 412 in all directions to some extent, to bediverged from the screen 410. With the rear-transmission type laserprojector 400, a person views pictures on the screen 410 from the frontof the screen 410 (on the side opposite to the laser projection unit).

As described above, according to the fourth embodiment, in therear-transmission type laser projector 400 which projects modulatedlaser beams that are outputted from the laser projection unit 50 on therear surface of the screen, the absorber 413 as the constituent of thescreen 410 has the transmission characteristics of transmitting, amongthe incident light, only three color (red, blue, and green) laser beamswhich are projected by the laser projection unit 50 and lights in theneighboring wavelength band, and lights in a wavelength band where theluminosity factor is significantly low. Therefore, it is possible toprevent pictures on the screen 410 from becoming hard to be seen due tothe indoor illumination or lights from outdoors.

Further, according to the fourth embodiment, the range of wavelengthswhich are transmitted through the absorber 413 of the screen 410 islonger than 3 nm and shorter than 10 nm with the respective wavelengthsof the laser beams outputted by the laser projection unit 50 being inthe center. Therefore, it is possible to efficiently transmit theprojected laser light beams through the screen 410 in consideration ofvariations in the wavelengths of the actual laser output lights, therebygreatly improving the contrast of pictures on the screen.

The rear projection type laser projector 400 also can utilize theillumination as described in the third embodiment. Accordingly, thecontrast of the pictures on the screen 410 can be further increased.

Embodiment 5

Hereinafter, a fifth embodiment of the present invention will bedescribed in FIG. 13.

In a laser projector 500 according to the fifth embodiment, picturesprojected on a screen are viewed by using a light transmitting member,such as glasses having specific light transmission characteristics.

FIG. 13 is a diagram for explaining the laser projector 500 according tothe fifth embodiment.

The laser projector 500 according to the fifth embodiment has a laserprojection unit 40 which outputs laser beams 41, a screen 610 onto whichthe laser beams 41 from the laser projection unit 40 are projected, andglasses 510 for observing pictures which are projected on the screen610. The laser projection unit 40 is identical to that of the laserprojector according to the second embodiment, and the screen 610 isidentical to that in the conventional laser projector.

In the fifth embodiment, the glasses 510 to be used for viewing thepictures on the screen 610 utilize a filter which transmits only laserbeams of three colors which are emitted from the respective lasers.

Next, the function and effect will be described.

Since, in the fifth embodiment, the glasses 510 to be used for viewingpictures on the screen 610 have a filter which transmits only laserbeams of three colors that are emitted from the respective lasers, thecontrast on the screen 610 when pictures on the screen are viewedthrough the glasses 510 is increased up to 100 even in a state where theindoor illumination 30 is turned on.

More specifically, according to this embodiment, only lights emittedfrom the lasers, i.e., light 511 with wavelengths near 660 nm, near 532nm, and near 457 nm can be viewed through the glasses, while lights withother wavelengths such as illumination light 32 reflected by the screenare cut out and do not come into sight.

While in this fifth embodiment the glasses are adopted as the lighttransmitting member that has specific light transmission characteristicsand is used for viewing pictures on the screen, the light transmittingmember is not limited to these glasses but may be anything that coversthe eyes, such as goggles.

Further, while the typical illumination such as a fluorescent lamp isemployed as the indoor illumination 30 in this fifth embodiment, laserswhich emit laser beams with wavelengths of 480 nm, 555 nm, and 630 nmmay be used as the indoor illumination. Since, in this case, theselectivity of wavelengths of the light transmitting member such asglasses is increased, the contrast of pictures on the screen 610 isimproved, and grayish-block phenomenon in pictures on the screen 610 canbe completely prevented. It goes without saying that the wavelengths ofthe laser beams herein used as the indoor illumination are not limitedto those described above.

Further, according to the fifth embodiment, the laser projector has thesame structure as that of the second embodiment, while the laserprojector according to the fifth embodiment may have the same structureas that of the conventional laser projector or the laser projectoraccording to the first embodiment. Alternatively, this laser projectormay have the same structure as that of the rear-transmission type laserprojector according to the fourth embodiment. Also in these cases, thesame effect can be obtained.

While in the above-mentioned embodiments the lasers 1, 2, and 3 of red,blue, and green as primary colors are employed as the short-wavelengthlaser sources, it is also possible to employ, for example, two lasers of450 nm and 490 nm as blue lasers, and consequently employ lasers of fourwavelengths in total. Further, a larger number of lasers may beemployed.

INDUSTRIAL AVAILABILITY

The laser projector according to the present invention is useful as onethat can achieve fine pictures of good contrast in locations where lightother than laser beams is applied on the screen.

1. A laser projector which modulates laser beams, and projects themodulated laser beams, comprising: short-wavelength laser sources thatemit at least laser beams of three colors of red, blue and green; amodulation unit that modulates the laser beams from the laser sources onthe basis of a picture signal; and a screen onto which the modulatedlaser beams are projected, wherein said screen has characteristics ofreflecting incident light such that reflection peaks for the incidentlight are located at wavelengths of the at least laser beams of threecolors of red, blue and green, which are emitted from theshort-wavelength laser sources, and at neighboring wavelengths, andwherein a projection room in which the screen is placed is illuminatedby illumination light that has significantly low levels of wavelengthcomponents corresponding to the wavelengths of the at least laser beamsof three colors of red, blue and green, which are emitted from theshort-wavelength laser sources.
 2. The laser projector as defined inclaim 1, wherein the screen has a reflector which reflects only the atleast laser beams of three colors of red, blue and green, which areemitted from the short-wavelength laser sources, and lights in aneighboring wavelength band.
 3. The laser projector as defined in claim2, wherein the neighboring wavelength band of the wavelengths of the atleast laser beams of three colors of red, blue and green, which arereflected by the reflector, has a range of longer than 3 nm and shorterthan 10 nm, with the wavelengths of the respective laser beams being ina center of the range.
 4. The laser projector as defined in claim 2wherein the reflector comprises a dielectric multilayer film.
 5. Thelaser projector as defined in claim 2 wherein the reflector is formedusing a hologram recording material.
 6. A laser projector whichmodulates laser beams, and projects the modulated laser beams,comprising: short-wavelength laser sources that emit at least laserbeams of three colors of red, blue and green; a modulation unit thatmodulates the laser beams from the laser sources on the basis of apicture signal; and a screen onto which the modulated laser beams areprojected, wherein said screen has characteristics of transmittingincident light such that transmission peaks for the incident light arelocated at wavelengths of the at least laser beams of three colors ofred, blue and green, which are emitted from the short-wavelength lasersources, and at neighboring wavelengths, and wherein a projection roomin which the screen is placed is illuminated by illumination light thathas significantly low levels of wavelength components corresponding tothe wavelengths of the at least laser beams of three colors of red, blueand green, which are emitted by the short-wavelength laser sources. 7.The laser projector as defined in claim 6, wherein said screen has anabsorber that transmits the at least laser beams of three colors of red,blue and green, which are emitted from the short-wavelength lasersources, and lights in a neighboring wavelength band, and lights in awavelength band where luminosity factor is significantly low.
 8. Thelaser projector as defined in claim 7, wherein the neighboringwavelength band of the wavelengths of the at least laser beams of threecolors of red, blue and green, which are transmitted by the absorber,has a range of longer than 3 nm and shorter than 10 nm, with thewavelengths of the respective laser beams being in a center of therange.
 9. The laser projector as defined in claim 7 wherein the absorberis formed by laminating plural filters each cutting out lights havingpredetermined wavelengths, among light incident on the absorber.
 10. Thelaser projector as defined in claim 6 wherein the laser sources arelocated on a rear side of the screen, and light projected from the lasersources on the screen is observed from a front side of the screen.